unable to make/receive calls or texts following 13.3 update

Hi there,

Two days ago my phone automatically updated to ios 13.3. Since then I've been unable to send or receive calls or texts, and have also had intermittent signal. I've contacted my network provider, who ran a diagnostics and assured me everything is okay from their end. I contacted apple support who told me to update my phone again via itunes. I've uninstalled and reinstalled itunes, and have restored a previous back-up of my phone. I have put it on aeroplane mode and back, switched it off and on, and I still can't make or receive calls/texts, despite me having a network connection with four bars. Any help before I throw the phone in the bin, would be greatly appreciated. A local apple authorised repairer wants $100 just to look at it, never mind fix it.